Symmetrical loop receiver



31' W 064 OR 1,920 665 I LM W Aug. 1, 1933. H. o. PETERSON 7 1,920,655

SYMMETRICAI LOOP RECEIVER E Filed April '2, 1925 INVENTOR HAROLD O. PETERSON usfralia 263/26- IZ/B/E E/L 4 A ORNEY UNITED STATES PATENT orrics.

SYMMETRICAL LOOP RECEIVER Harold 0. Peterson, Riverhead, N. Y., assignor to Radio Corporation of America, a Corporation of Delaware Application April 2, 1925. Serial No. 20,052

Claims.

which signals are sent or received, to eliminate vertical antenna effects in circuits arranged for use in direction finding and to simplify the controls.

In the carrying out of my invention use is made of amplifiers and when so used with high frequency circuits the neutralization of tube capacity effects is very advisable if not indispensable. With my arrangement the input and'output circuits of two tubes used are balanced and a single means for doing both for each tube is used. Further advantages from my invention not possible formerly with high frequencies on account of above mentioned tube capacities, is the elimination of effects from harmonics of these frequencies by balancing one tube against the other so that only the fundamental will be amplified.

Also, my device prevents distortion and allows the tubes used to be worked to a higher percentage, of load than formerly. The neutralizing of input and output circuits of the balanced tubes is advantageous for various reasons. It allows the use of the circuit to a considerably higher degree of efficiency, aids in eliminating harmonics, increases the selectivity and in general permits the practical use of higher frequencies than has hitherto been possible. The arrangement so used might be called what is commonly known as a fpush pull amplifier, neutralized.

To reach the neutral point two vacuum tubes are used which are preferably of identical characteristics and any bias potentials on the grids of the tubes are preferably equal. These devices using grid, plate and filament are liable to oscillate of their own accord when certain values of inductance or capacity are introduced between them. This invention provides means for connecting the grid and plate circuits with means for balancing any tendency so originating.

This invention relates to the use of a so-called loop antenna in which the circuit of the loop is made entirely symmetrical with respect to the ground or counterpoise systems and feeding back to the ground or counterpoise system any electrostatic energy that is developed on either side of the loop without effecting the directional or electro-magnetic function. This absolute symmetry has hither-to been impossible because it has not been possible to neutralize the radio frequency necessarily used in the amplifier and loop. Still another object is to positively separate the directional oscillations and the oscillations caused by vertical antenna effect and combine them in such a way as to positively determine the direction from which the oscillations are sent or received. This is accomplished by maintaining a balance between the two sides of the loop by connecting the middle of the loop to ground. Also I am able to vary the shape and characteristic of any receiving diagram by my method.

have been used that the two sides of the loop are unbalanced with respect to ground. Various methods have been used to remedy this by balancing condensers, or inductances which require more or less expert manipulation. My invention overcomes this diificulty and the only restriction on perfect operation lies in the original construction. No balancing with a shift ofpositions or tuning is necessary and any so-called, direct effect or effect of reception on the amplifier structure can be prevented by shielding.

Thus, the two eifects on the loop aerial can be definitely separated. Since this is true they can also be combined by my method thereby producing an unidirectional loop Whose receiving diagram is the familiar cardoid or heart shape, having only one side at which no reception or sending of signals can be had. This can also be varied or changed by changing the coupling arrangement to magnify one or the other component.

For further, more definite objects, reference is made to the appended claims and the annexed specification and drawing will furnish a better understanding and working of my invention.

Fig. 1 shows a conventional hook-up with my invention.

Fig. 2 shows a modification having means for preventing oscillation and combining the electrostatic and electro-magnetic effects on the loop to produce a receiving diagram of a cardoid nature. 7

Fig. 3 shows a modification for sending.

In Fig. 1, M is the loop or antenna of one or more convolutions of wire encircling an appreciable area and the separate wires are spaced I slightly apart. A condenser C is connected across the loop to provide an oscillatory circuit which effects the grids of tubes A and B connected on either side of the loop. The plates of tubes A and B are respectively connected on either side of a tuned primary P of a transformer, the midpoint of whose winding is in series with a high potential generator H which 6 It has been found that when loops in general T the tickler coil connected to the plate of tube D and phones P. The filaments of tubes A and B are grounded at G and the electrical midpoint of loop M is grounded at G Thus it can be seen that anyoscillations set up instantaneously in both sides of the loop at the same time will cause current to flow from grid of A and B simultaneously through primary P to the filaments of the tubes, but since the currents are flowing in opposite directions their resultant is zero.

To put it another way, when voltages are induced in the loop M by electro-static or vertical antenna effects it will swing the grids of tubes A and B positive with respect to ground. The result of these voltages due to vertical antenna effects will be to simultaneously increase or decrease theplate currents of tubes A and B. The voltage induced in the secondary S by a simultaneous increase in plate current of tube A will be 180 degrees out of phase with the voltage induced in the secondary S by a simultaneous increase in the plate current of tube B. If the plate currents of both tubes A and B are simultaneously increased or decreased by equal amounts, the resultant voltage induced in the secondary S will be zero.

Therefore, since the potentials of the grids of tubes A and B with respect to their filaments are increased or decreased simultaneously by equal amounts due to electro-static or vertical antenna effects, the resultant voltage induced in the secondary S by these effects will be zero from this effect.

In the same way, voltages are induced in the loop M by loop antenna effect to cause an alternating current of signal wave frequency to flow into the tuned loop circuit through condenser C This circulating current through C will cause an alternating voltage to be impressed first on tube A and then on tube B both being of equal magnitude and 180 degrees out of phase with each other. This will cause the plate current of tube A to increase at the instant it causes the plate current of tube B to decrease. The voltages in duced in the secondary by these changes in the two plate currents will be in phase with each other. Hence, the circulating or loop voltage will establish an alternating potential difierence between the terminals of the secondary S which may be detected by one of the many known methods, as, the one shown having a simple detector circuit of a regenerative character. It is not intended to limit the use of this arrangement with this particular detector but it can be used with any other type already known or a sending set may be used with the slight re-arrangement shown in Fig. 3. Thus, it can be seen that the directional voltages can be entirely separated from any non-directional or static voltages and that no adjustments or regulations are necessary to do this depending upon the position of the loop M with respect to ground, and also that the symmetrical loop has an entirely symmetrical effect on the primary winding P of the transformer since the wire W is taken off at the electrical mid-point of the transformer. The o y limitation of this arrangement being the original construction, inequalities and variations of the antenna might be compensated for by slight variations or deviations from the center of the connection of wire W to transformer P or by any other feasible method. When once proper- 1y adjusted no more regulation is necessary as inequalities are automatically compensated for by the symmetry of the system. It would also add to the efficiency and ease of operation to have coils of P as closely coupled as is possible. The coils of the loop antenna M are so close together in respect to the area enclosed. as to make any leakage flux negligible.

Owing to the liability of the plate and gridcircuits to oscillate due to voltages developed locally my arrangement as shown in Fig. 2 is used. It is known that when a capacity is inserted in a circuit containing one tube arranged as a simple oscillator, that is equal and opposite in effect to the natural capacity of the plate and grid circuit, no oscillations will occur. However when two tubes are used as in my arrangement a difierent problem arises as to how to connect the condensers to efiiciently prevent oscillation.

In my invention I couple the grid of one tube to the plate of the other and vice versa. But since the respective grids of these tubes are connected to either side of the loop M and the respective plates are connected to either side of the inductance P there are symmetrical circuits equal and opposite in potential effect for instantaneous values occurring on both sides of the loop and winding P at the same time. The condenser CB provides a means for preventing tube B from oscillating and CA. tube A and vice versa dependent upon whether the grid or plate circuit is traced. At X part of the current will flow to the grid of tube A and part of the current will flow to the condenser CB. At Y part of the current will flow to the grid of B and part to CA. Then if CA equals the plate to grid capacity of A, and CB equals the plate to grid capacity of B then the balance will be maintained on the grids and plates about the ground G1 of loop M or about G2. Of course G2 is the same electrically as G1 so that the same is true of it. Thus condensers CA and CB serve a double purpose. Any suitable receiving means may be added to secondary S Any lack of symmetry of the system may be com pensated for by varying CA, CB, the position of tap W or 0. These devices may be varied separately or simultaneously to control the arrangement to keep the tubes properly balanced.

Fig. 2 also shows my device wherein use is made of the capacity or antenna eifect on the loop. It is the same as in Fig. 1. like symbols representing like elements, except that N is introduced in the ground circuit to the loop, which is a variable inductance or other well-known tuning means.

This can be used to tune the static or vertical antenna efiect component of the signals. Advantage is taken of the oscillations caused in the circuit by these signals by the introduction of primary P of a second transformer in the wire W. This might be either side of battery H in respect to P the secondary of this second transformer, is connected in series or in any other manner so as to effect the secondary circuit with S Preferably the coupling P S is variable. Some means should be used to effect the proper phase relation between the currents in S and S as resistance, condensers or a phase shifter. P S may be made variable instead of l? S to increase or decrease the volume. Condensers and inductances in any of the various circuits may also be used to produce the proper coupling.

Now when a wave impinges on the loop M the resultant of both the plain antenna or capacity effect and the loop effect will be registered in the circuits S S Thus with proper adjustment the loop circuit becomes uni-directional, and if the intensity of signal be plotted on circular coordinates against position of loop M a cardoid or heart-shaped diagram will result. This will be true when the intensity of signal from the static component is equal in effect to the maximum value of the directional component.

If the voltage of secondary S is zero then the receiving diagram will be a figure 8. If the voltage of the secondary S is zero in a l positions of the loop M then the receiving diagram will be a circle. By varying the couplings and values of intensity of signal by tuning, etc. various shaped diagrams may be obtained.

It is obvious that the various modifications herein shown may be combined or altered in any degree to obtain results commensurate with the purpose of the invention. For instance the variations shown in Figs. 1 and 2 may be combined without appreciable changes. Or any one, or more than one of the various modifying elements may be omitted, as one or the other of condensers CA or CB may be omitted.

Fig. 3 shows the same arrangement with a few changes necessary to use it with a sending set, the difierence being that the tube connections are reversed. Its operation is thought to be obvious so that discussion of the receiving arrangement will suflice for both. The oper ation of the device may be well described by reference to Fig. 2. The operation of the devices shown in Fig. 1 is similar to this except that no tuning for the static or non-directional component is made, and only the directional waves are received.

Whenever it is desired to determine the direction, from which a' message is received or to which a message is sent the condenser C may be set to tune the loop M to the proper wave length and the tuner N set to correspond in wave length. The couplings between the primariesand the secondaries can then be varied so that the maximum obtainable directional component and the non-directional component are equal. Then the rotation of loop M through the space of a small angle will give no resulting oscillation but anywhere outside this angle the oscillations will increase up to apoint 180 from .the middle of this angle where it will be a maxi- 'mnm. This is the result of the cardoid receiving or sending diagram. By increasing or decreasing the coupling at either transformer or changing the tuning various results can be effected.

Fig. 1 shows an ordinary receiving arrangement the operation of which is well known and obvious. In this figure primary tuning condenser C is shown to tune the transformer ac cording to different frequencies. It is clear that tuning condensers might equally well be applied -to the transformers of Fig. 2. Also condensers might be well used between the outside taps of primary 3: and the middle tap W to compensate for any variations in the circuit or they might be used for turing as well.

It is clear from this disclosure that this arrangement need not be limited to use of a single loop. A double loop or two separate loops in series might equally well be used if they are equal in size. Also whenever use is made of the nondirectional or static component a separate antennae might be connected on at 0.

Having thus described my invention I wish to be limited only to the broadest elements of the disclosure and by the prior art as set up in the appended claims.

1. A method of developing oscillations consisting of balancing the oscillations in a loop by dividing the loop circuit into symmetrical circuits, conducting the oscillations from either side of the loop to an element of a thermionic relay, and by-passing part of the oscillations to a different element of another thermionic relay, whereby the local oscillations set up by either thermionic relay are neutralized.

2. In combination an electrostatic tuner, an electromagnetic tuner, a circuit for electromagnetic oscillations, comprising a loop connected to two thermionic relays in circuit with translating means, a circuit for electrostatic oscillations comprising the conductors of the loop providing two parallel paths to the thermionic relay connected to a single conductor, and a separate translating device whereby the two oscillations may be made to act separately, and means to'neutralize capacity effects originating in the thermionic relays thus connected.

3. In combination an electro-static tuner, an electromagnetic tuner, a circuit for electromagnetic oscillations comprising a loop connected to two thermionic relays in circuit with translating means, a circuit for electrostatic oscillations comprising the conductors of the loop providing two parallel paths to the thermionic relays connected to a single conductor and a separate translating device, whereby the two oscillations may be made to act separately.

4. A method of developing oscillations consisting of conducting non-directional and directional oscillations over two symmetrical paths and combining them to neutralize the non-directional oscillations and amplify the directional oscillations.

5. A directional system having a loop antenna grounded at the mid-point, tuning means connected between the ends of the loop and a pair of three element valves having their grids connected respectively to the ends of the loop, their cathodes connected together and their anodes connected through an impedance, an inductance connected between the mid-point of said impedance and the cathodes, and means for coupling a receiver to said impedance and said inductance.

6. A directional system having a loop antenna grounded at the mid-point, tuning means connected between the ends of the loop and a pair of three element valves having their grids coupled respectively to the ends of the loop, their cathodes connected together, their anodes connected through an impedance, an inductance connected between the mid-point of said impedance and the cathodes, a tuning condenser in shunt to said impedance, and means for utilizing the voltage oscillations appearing across said impedance and said inductance.

7. In a radio signalling device, a loop aerial, an inductance having one end connected to the mid-point of said loop and the other end grounded, a condenser connected across the ends of said loop, a pair of vacuum tubes, a connection between one end of said loop and the grid of one of said vacuum tubes, a connection between the other end of said loop and the grid of the other vacuum tube, a plate circuit for each of said vacuum tubes comprising a portion of a tapped inductance, a separate inductance and a source of potential common to both plate circuits, and means for utilizing the oscillations at signal frequency appearing across one or both of said inductances.

8. In a directional receiver, a loop circuit having its mid-point grounded, a vacuum tube amplifier connected to each end of said loop, plate circuits for said amplifiers including a tapped inductance having a portion thereof in each plate circuit, a grounded filament heating circuit common to the filaments of both of said vacuum tubes, a separate inductance connected between the, tap on said plate circuit inductance and the filament heating circuit, and means for variably coupling a receiver to said inductance.

9. In combination two symmetrical circuits having common returns comprising a loop the mid-point of which is connected to one of said common returns, tuning means in said common return, a capacity connected across the ends of said loop, a vacuum tube amplifier for each of said symmetrical circuits, means for associating the grid of each of said amplifiers with opposite ends of said loop, a filament heating circuit common to both of said amplifiers connected to the other of said returns, an inductance electrically equal portions of which are in the plate circuit of each of said amplifiers, a separate inductance and a source of potential connected between the electrical mid-point of said plate inductance and the filament heating circuit, and means for utilizing the voltage oscillations appearing in said last named inductances.

10. In a directional aerial system, a loop antenna, a variable condenser in series therewith, a connection between the electrical midpoint of said loop and ground, a variable inductance in said connection, a pair of thermionic tubes each having cathode, anode and control electrodes, grounded heating means for said cathode, a connection between one terminal of said condenser and the control electrode of one of said tubes,

- a connection between the other terminal of said condenser and the control electrode of the other of said tubes, a capacity connected between the first named terminal of said condenser and the anode of said last named tube and a capacity connected between the second named terminal of said condenser and the anode of said first named tube.

11. In a directional aerial system, a loop antenna, a variable condenser in series therewith, a connection between the electrical midpoint of said loop and ground, a pair of thermionic tubes each having cathode, anode and control electrodes, grounded heating means for said cathodes, a connection between one terminal of said variable condenser and the control electrode of one of said tubes, a connection between the other terminal of said variable condenser and the control electrode of the other of said tubes, a transformer having a secondary winding and a symmetrical tapped primary winding connecting the anodes of said tubes, an inductance connected between said tap and the cathodes of said tubes, a second inductance in series with the secondary winding of said transformer coupled to said first named inductance, and means for connecting said last named circuit to receiving apparatus.

12. In radio apparatus in combination, a loop antenna in series with a variable condenser, a

receiver, and means for obtaining directional effeet and sense of direction in said receiving circuit including a pair of thermionic tubes each having anode, cathode and grid electrodes, a connection between the electrical midpoint of said loop and ground, a connection between one terminal of said condenser and the grid electrode of one of said tubes, a connection between the other terminal of said condenser and the grid electrode of the other of said tubes, a grounded heating circuit for the cathodes of said tubes, a transformer having a symmetrically tapped primary winding, means for connecting the anodes of said tubes to opposite ends of said primary winding, an inductance connected between said tap and the cathodes of said tubes, and an input circuit for said receiver including the secondary winding of said transformer in series with an inductance coupled to said first named inductance the degree of coupling between said inductances being utilized to determine the angular elevation of the source of signals to which the receiver is tuned.

13. Directional radio apparatus including a composite aerial system having two degrees of oscillatory freedom one of which allows it to respond to the electric field of the signal, the other of which allows it to respond to the magnetic field of the signal, indicating apparatus, a thermionic relay having its input circuit connected to said system and its output system connected to said indicator, means in said output circuit for impressing signals characteristic of one or both of said fields on said indicator and means for continuously maintaining the efiect of the magnetic field on said system symmetrical with respect to the efiect of the electrical efiect on said system while signals characteristic of one or both of said fields are impressed on said indicator.

14. A directional radio system comprising component systems having different directional characteristics, means for afiecting electric symmetry between said component systems, means for amplifying the high frequency energy in both of said systems, a receiver, and means for impressing energy from each of said component systems on said receiver during maintenance of symmetry between them.

15. A directional radio system comprising a closed circuit including a rotatable coil, an antenna path, means for affecting electric symmetry of said closed circuit with respect to said antenna path, a thermionic relay having input elements connected with said closed circuit and said path, an indicator, means for impressing energy from said closed circuit on said indicator and means for impressing energy from said antenna path upon said indicator while said closed circuit is maintained symmetrical with respect to said antenna path.

16. A directional radio receiving system comprising a closed circuit including a rotatable coil, means for tuning the closed circuit, an antenna path, means for effecting symmetry of said closed circuit with respect to said antenna path, a pair of three electrode thermionic devices, means associated therewith for causing their grids to be affected in opposite senses by the current in said closed circuit and in similar senses by the current in said antenna path, an output circuit for said thermionic devices, an indicator, means in said output circuit for transferring energy representative of the current in said closed circuit to said indicator and means in said output circuit for transferring energy representative of the current in said antenna path to said indicator.

17. The method of determining the sense of direction of a source of electro-radiant energy by utilization of a plurality of electrical systems having different directional characteristics and one of which is electrically symmetrical with respect to another which comprises, cumulatively affecting a translating device by components of energy from one of said systems, moving a part of said system to obtain the direction of the source of radiant energy, diiferentially and cumulatively affecting said translating device by components of energy from both of said systems, moving a part of said first named system to vary the magnitude of said indication, determining from the sense of the change of said magnitude the sense of direction of said source of electro-radiant energy, and maintainingsymmetry between said electrical systems during said entire operation.

18. The method of determining the sense of direction of a source of electro-radiant energy by utilization of a plurality of electrical systems having difierent directional characteristics and one of which is electrically symmetrical with respect to another, which comprises amplifying the energy of both of said systems, producing an indication by the resultant of the energy in one of said systems, to determine the direction of the source 01 radiant energy, producing an indication by the resultant of the energies in both of said systems, moving a part of one of said systems to vary the magnitude of said indication, determining from the sense of the change of said magnitude the sense of direction of said source of electro-radiant energy, and maintaining symmetry between said electrical systems during said direction determining operation and said sense of direction determining operation.

19. The combination of a frame aerial, a pair of thermionic tubes having their control grids connected to the terminals of said frame aerial,

and their anodes connected together, and a capacity connecting the anode of each of said tubes to the control grid of the other of said tubes.

20. In a directional receiver, a directional aerial comprising one or more turns of wire, a variable condenser in series therewith, a connection between the electrical center of said aerial and ground, a reactance in said connection, a pair of thermionic tubes, each having electrodes including anode, cathode and control grid, a circuit grounding said cathodes, a connection between one terminal of said variable condenser and the control grid of one of said tubes, a connection between the other terminal of said HAROLD o. PETERSON. 

